Question: Simplify the following expression: $z = \dfrac{y}{4} - \dfrac{y}{7}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4$ and $7$ $\lcm(4, 7) = 28$ $ z = \dfrac{7}{7} \cdot \dfrac{y}{4} - \dfrac{4}{4} \cdot \dfrac{y}{7} $ $z = \dfrac{7y}{28} - \dfrac{4y}{28}$ $z = \dfrac{7y -4y}{28}$ $z = \dfrac{3y}{28}$